349 lines
8.2 KiB
Go
349 lines
8.2 KiB
Go
// Copyright 2011 Miek Gieben. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// DNS server implementation.
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package dns
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import (
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"io"
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"os"
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"net"
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)
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// how to do Tsig here?? TODO(mg)
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type Handler interface {
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ServeDNS(w ResponseWriter, r *Msg)
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// IP based ACL mapping. The contains the string representation
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// of the IP address and a boolean saying it may connect (true) or not.
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}
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// A ResponseWriter interface is used by an DNS handler to
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// construct an DNS response.
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type ResponseWriter interface {
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// RemoteAddr returns the net.Addr of the client that sent the current request.
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RemoteAddr() net.Addr
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// Write a reply back to the client.
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Write([]byte) (int, os.Error)
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}
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// port?
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type conn struct {
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remoteAddr net.Addr // address of remote side (sans port)
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handler Handler // request handler
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request []byte // bytes read
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_UDP *net.UDPConn // i/o connection if UDP was used
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_TCP *net.TCPConn // i/o connection if TCP was used
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hijacked bool // connection has been hijacked by hander TODO(mg)
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}
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type response struct {
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conn *conn
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req *Msg
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}
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// ServeMux is an DNS request multiplexer. It matches the
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// zone name of each incoming request against a list of
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// registered patterns add calls the handler for the pattern
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// that most closely matches the zone name.
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type ServeMux struct {
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m map[string]Handler
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}
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// NewServeMux allocates and returns a new ServeMux.
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func NewServeMux() *ServeMux { return &ServeMux{make(map[string]Handler)} }
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// DefaultServeMux is the default ServeMux used by Serve.
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var DefaultServeMux = NewServeMux()
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// The HandlerFunc type is an adapter to allow the use of
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// ordinary functions as DNS handlers. If f is a function
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// with the appropriate signature, HandlerFunc(f) is a
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// Handler object that calls f.
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type HandlerFunc func(ResponseWriter, *Msg)
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// ServerDNS calls f(w, r)
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func (f HandlerFunc) ServeDNS(w ResponseWriter, r *Msg) {
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f(w, r)
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}
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// Helper handler that returns an answer with
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// RCODE = refused for every request.
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func Refused(w ResponseWriter, r *Msg) {
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m := new(Msg)
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m.SetRcode(r, RcodeRefused)
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buf, _ := m.Pack()
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w.Write(buf)
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}
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// RefusedHandler returns HandlerFunc with Refused.
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func RefusedHandler() Handler { return HandlerFunc(Refused) }
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// ...
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func ListenAndServe(addr string, network string, handler Handler) os.Error {
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server := &Server{Addr: addr, Net: network, Handler: handler}
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return server.ListenAndServe()
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}
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func (mux *ServeMux) match(zone string) Handler {
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var h Handler
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var n = 0
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for k, v := range mux.m {
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if !zoneMatch(k, zone) {
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continue
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}
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if h == nil || len(k) > n {
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n = len(k)
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h = v
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}
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}
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return h
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}
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func (mux *ServeMux) Handle(pattern string, handler Handler) {
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if pattern == "" {
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panic("dns: invalid pattern " + pattern)
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}
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// Should this go
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//if pattern[len(pattern)-1] != '.' { // no ending .
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// mux.m[pattern+"."] = handler
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//} else {
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mux.m[pattern] = handler
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}
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func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
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mux.Handle(pattern, HandlerFunc(handler))
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}
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// ServeDNS dispatches the request to the handler whose
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// pattern most closely matches the request message.
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func (mux *ServeMux) ServeDNS(w ResponseWriter, request *Msg) {
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h := mux.match(request.Question[0].Name)
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if h == nil {
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h = RefusedHandler()
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}
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h.ServeDNS(w, request)
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}
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// Handle register the handler the given pattern
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// in the DefaultServeMux. The documentation for
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// ServeMux explains how patters are matched.
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func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
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func HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
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DefaultServeMux.HandleFunc(pattern, handler)
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}
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// A Server defines parameters for running an DNS server.
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// Note how much it starts to look like 'Client struct'
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type Server struct {
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Addr string // address to listen on, ":dns" if empty
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Net string // if "tcp" it will invoke a TCP listener, otherwise an UDP one
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Handler Handler // handler to invoke, dns.DefaultServeMux if nil
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ReadTimeout int64 // the net.Conn.SetReadTimeout value for new connections
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WriteTimeout int64 // the net.Conn.SetWriteTimeout value for new connections
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TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>
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}
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// ...
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func (srv *Server) ListenAndServe() os.Error {
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addr := srv.Addr
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if addr == "" {
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addr = ":domain"
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}
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switch srv.Net {
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case "tcp", "tcp4", "tcp6":
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a, e := net.ResolveTCPAddr(srv.Net, addr)
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if e != nil {
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return e
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}
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l, e := net.ListenTCP(srv.Net, a)
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if e != nil {
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return e
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}
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return srv.ServeTCP(l)
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case "udp", "udp4", "udp6":
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a, e := net.ResolveUDPAddr(srv.Net, addr)
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if e != nil {
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return e
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}
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l, e := net.ListenUDP(srv.Net, a)
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if e != nil {
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return e
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}
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return srv.ServeUDP(l)
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}
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return nil // os.Error with wrong network
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}
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func (srv *Server) ServeTCP(l *net.TCPListener) os.Error {
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defer l.Close()
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handler := srv.Handler
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if handler == nil {
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handler = DefaultServeMux
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}
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forever:
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for {
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rw, e := l.AcceptTCP()
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if e != nil {
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return e
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}
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if srv.ReadTimeout != 0 {
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rw.SetReadTimeout(srv.ReadTimeout)
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}
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if srv.WriteTimeout != 0 {
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rw.SetWriteTimeout(srv.WriteTimeout)
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}
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l := make([]byte, 2)
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n, err := rw.Read(l)
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if err != nil || n != 2 {
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continue
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}
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length, _ := unpackUint16(l, 0)
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if length == 0 {
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continue
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}
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m := make([]byte, int(length))
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n, err = rw.Read(m[:int(length)])
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if err != nil {
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continue
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}
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i := n
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for i < int(length) {
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j, err := rw.Read(m[i:int(length)])
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if err != nil {
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continue forever
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}
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i += j
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}
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n = i
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d, err := newConn(rw, nil, rw.RemoteAddr(), m, handler)
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if err != nil {
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continue
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}
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go d.serve()
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}
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panic("not reached")
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}
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func (srv *Server) ServeUDP(l *net.UDPConn) os.Error {
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defer l.Close()
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handler := srv.Handler
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if handler == nil {
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handler = DefaultServeMux
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}
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for {
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m := make([]byte, DefaultMsgSize)
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n, a, e := l.ReadFromUDP(m)
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if e != nil {
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return e
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}
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m = m[:n]
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if srv.ReadTimeout != 0 {
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l.SetReadTimeout(srv.ReadTimeout)
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}
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if srv.WriteTimeout != 0 {
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l.SetWriteTimeout(srv.WriteTimeout)
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}
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d, err := newConn(nil, l, a, m, handler)
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if err != nil {
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continue
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}
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go d.serve()
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}
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panic("not reached")
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}
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func newConn(t *net.TCPConn, u *net.UDPConn, a net.Addr, buf []byte, handler Handler) (*conn, os.Error) {
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c := new(conn)
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c.handler = handler
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c._TCP = t
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c._UDP = u
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c.remoteAddr = a
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c.request = buf
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return c, nil
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}
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// Close the connection.
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func (c *conn) close() {
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switch {
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case c._UDP != nil:
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c._UDP.Close()
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c._UDP = nil
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case c._TCP != nil:
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c._TCP.Close()
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c._TCP = nil
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}
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}
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// Serve a new connection.
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func (c *conn) serve() {
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for {
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// Request has been read in ServeUDP or ServeTCP
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w := new(response)
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w.conn = c
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req := new(Msg)
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if !req.Unpack(c.request) {
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// Send a format error back
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x := new(Msg)
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x.SetRcodeFormatError(req)
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buf, _ := x.Pack()
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w.Write(buf)
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break
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}
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w.req = req
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c.handler.ServeDNS(w, w.req) // this does the writing back to the client
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if c.hijacked {
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return
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}
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break // TODO(mg) Why is this a loop anyway
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}
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if c._TCP != nil {
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c.close() // Listen and Serve is closed then
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}
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}
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func (w *response) Write(data []byte) (n int, err os.Error) {
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switch {
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case w.conn._UDP != nil:
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n, err = w.conn._UDP.WriteTo(data, w.conn.remoteAddr)
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if err != nil {
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println(err.String())
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return 0, err
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}
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case w.conn._TCP != nil:
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// TODO(mg) len(data) > 64K
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l := make([]byte, 2)
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l[0], l[1] = packUint16(uint16(len(data)))
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n, err = w.conn._TCP.Write(l)
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if err != nil {
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return n, err
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}
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if n != 2 {
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return n, io.ErrShortWrite
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}
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n, err = w.conn._TCP.Write(data)
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if err != nil {
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return n, err
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}
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i := n
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if i < len(data) {
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j, err := w.conn._TCP.Write(data[i:len(data)])
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if err != nil {
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return i, err
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}
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i += j
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}
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n = i
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}
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return n, nil
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}
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// RemoteAddr implements the ResponseWriter.RemoteAddr method
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func (w *response) RemoteAddr() net.Addr { return w.conn.remoteAddr }
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